As is known, currently marketed compact, portable electric arc welding machines are normally designed for MIG (Metal Inert Gas), MAG (Metal Active Gas), TIG (Tungsten Inert Gas), STICK or MMA (Metal Manual Arc) welding or any combination of these, and comprise a torch or welding gun designed for manual manipulation by the operator for manual welding, and an electric power unit connected electrically to the torch or gun by a connecting cable to supply the torch or gun with electric welding power with real-time control of voltage and current supply. The electric power unit is also designed to supply the torch or gun over the same connecting cable with the inert gas and metal filler wire used in some of the welding processes mentioned above.
More specifically, the electric power unit of welding machines of the above type substantially comprises an electric power converter, which draws electrical energy from the mains and converts it to electrical energy suitable for supply to the torch or gun, i.e. electrical energy with voltage and current values varying in real time as a function of demand by the welding process being performed; and a wire-feed device for supplying the torch, along the connecting cable, with a metal wire for MIG or MAG welding. The electric power unit of arc welding machines of the type in question also comprises a cooling unit for circulating coolant through the whole of the connecting cable and the torch to remove surplus heat produced in the cable and torch and so keep the torch and the connecting cable below a predetermined maximum temperature; and possibly also a pressurized-gas tank, with regulating valves, for storing the inert-gas mixture for supply, when needed and again along the connecting cable, to a diffuser integrated in the torch.
In compact, portable electric arc welding machines, the electric power converter, the wire-feed device, the cooling unit, and, in some cases, also the inert-gas tank and relative regulating valves, are fixed to a single supporting frame with wheels on which it rests on the floor, so that the electric power unit as a whole can be moved easily from one workplace to another.
Needless to say, the electric power unit, the torch or gun, the relative connecting cable, and the work grounding cable are designed to permit continuous operation of the machine at maximum power output.
In other words, the component parts of the electric power converter, the torch or gun, and the sections of the grounding cable and the electric cables integrated in the cable connecting the electric power unit and the torch, are all designed to continuously withstand the thermal stress produced by electric current flow in the machine operating at maximum power.
In the case in question, torches, guns, electric cables, and electric power converter components are designed to prevent overheating resulting in operating temperatures endangering the operator and/or the structural integrity of the machine.
Though excellent in terms of operation, welding machines of the above type have never been particularly versatile when the work calls for replacing the torch or gun and/or the electric power unit connecting cable. In which case, the original torch or gun must be replaced with a similar product capable of safely withstanding the maximum electric current output of the machine.
Given the difficulty, however, frequently encountered in procuring commercial torches, guns and/or connecting cables capable of withstanding the same current rating, most users, to be on the safe side, opt for commercial torches, guns and connecting cables with a higher current rating than specified for the machine.
Needless to say, component weight, size and cost increase in proportion to the current rating, so that oversizing the torches, guns and cables makes the machine harder to handle and greatly increases working cost.